Add support for outrigger.yml in addition to .outrigger.yml.

[grayside]

Using .outrigger.yml instead of the unhidden outrigger.yml seems like it was a mistake.

• Copy operations can leave behind a key piece of project configuration.
• Lack of visibility makes examining this file a lower priority, but it is key in understanding basic operations.

This change preserves the lookup capability for existing projects, but now gives priority to the new file name.